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<H2><A NAME="SECTION00681000000000000000"> </A>
<A NAME="ccd:input-and-output"> </A>
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Input and Output
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The <TT>COMBINE/CCD</TT> command offers the possibility to combine a number
of input images using different combining methods. <TT>COMBINE/CCD</TT>
takes three input parameters at maximum: the exposure type of the
images to be combined, the input frames themselves and and output
frame. The various command options can be chosen by setting a number
of specific keywords.
<P>
The first input parameter should contain the exposure type of the
images to be combined. Possible choices are: BS (for bias); FF (for
flat fields), DK (for dark), SK (for sky images), and OT (for others).
The combining options the command offers are controlled by a set of
exposure type dependent keywords, all starting with this two letter
identification that has been given as the first input parameter. These
keywords control various combining methods, scaling and offset
corrections, as well as weighting (see below).
<P>
The second input parameter is the input frames to combine. The input
can be provided in different ways:
<DL COMPACT>
<DT>1.
<DD>by a list of images; e.g. <TT>frame01,frame02,frame03</TT>;
<DT>2.
<DD>by a MIDAS catalogue; e.g. <TT>framecat.cat</TT>;
<DT>3.
<DD>by a MIDAS Data Organizer (DO) output table (with the
extension <TT>.tbl</TT>), the Association
Table (see Section <A HREF="node40.html#ccd:ccd-association-table">3.6.3</A>).
</DL>
The parameter for the output frame is required in case the input for
the second parameter is a catalogue or a string of input frames.
In the case of DO input (association) table, from the name of the
output calibration frame in the table the command extracts the
names of all requested single calibration frames and combines these
frames in the output frame. The name of the output master frame can
be indicated with an asterisk, meaning that all associated single
calibration frames have to be combined. In that case the names of
these single frames are taken for the calibration column in the
Association Table, <I>e.g.</I> <TT>BIAS</TT>, <TT>DK</TT>, etc. See also
Section <A HREF="node40.html#ccd:ccd-association-table">3.6.3</A>. By default, the input is
taken from the keyword <TT>CCD_IN</TT>.
In addition to the output calibration frame the combined sigma frame can be
generated. This frame is the standard deviation of the input frames about
the output frame.
<P>
Before the actual combining is done the exposure type descriptors of the
input frames are compared with the descriptor type stored in the
keyword <TT>`exp'_TYP</TT>. In case this keyword is filled with `*'
or `?' all exposure types are allowed. Else, a fatal error will
follow if the keyword content is not equal to the exposure type(s)
of one or more input frames.
<P>
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<ADDRESS>
<I>Petra Nass</I>
<BR><I>1999-06-15</I>
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